Primary aldosteronism is a secondary hypertension characterized by high blood pressure, high blood aldosterone, low renin, and low blood potassium due to adrenocortical hyperplasia or adenoma. Patients have moderately to severely elevated blood pressure, respond poorly to general antihypertensive medications, and some patients have considerable fluctuations in blood pressure, similar to the manifestations of pheochromocytoma. Patients with primary aldosteronism adrenal adenomas are generally small, with several clinical studies finding that 20%-85% of adenomas are less than 1 cm in diameter. pheochromocytomas are generally larger and can be differentiated by simultaneous blood MN and NMN measurements. Plasma renin levels tend to be high in patients with pheochromocytoma and may be related to stimulation by high catecholamines and hypovolemia. Pheochromocytoma may also secrete renin abnormally. Patients also have elevated plasma standing and recumbent aldosterone concentrations. Hypokalemia can occur because catecholamines can contribute to the entry of potassium ions into the cells and the increase of renin and aldosterone.